Apparatus and method for allocating resources in a single carrier-frequency division multiple access system

ABSTRACT

An apparatus and method for allocating resources in an Single Carrier-Frequency Division Multiple Access (SC-FDMA) communication system are provided, in which a Node B performs inter-subband hopping on a resource unit for a User Equipment (UE) on a frequency axis along which at least two subbands are defined, at each predetermined hopping time, determines whether to turn on or off mirroring in a subband having the hopped resource unit on a cell basis at the each hopping time, selects a resource unit by selectively mirroring the hopped unit according to the determination, and allocates the selected resource unit to the UE.

PRIORITY

This application claims priority under 35 U.S.C. § 119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onJan. 9, 2007 and assigned Serial No. 2007-2657, a Korean PatentApplication filed in the Korean Intellectual Property Office on Jun. 14,2007 and assigned Serial No. 2007-58331, a Korean Patent Applicationfiled in the Korean Intellectual Property Office on Aug. 9, 2007 andassigned Serial No. 2007-80204, and a Korean Patent Application filed inthe Korean Intellectual Property Office on Dec. 7, 2007 and assignedSerial No. 2007-126476, the entire disclosure of any of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for efficientlyallocating control channel transmission resources when a packet datachannel and a control channel are transmitted in the same transmissionperiod in a Single Carrier-Frequency Division Multiple Access (SC-FDMA)wireless communication system.

2. Description of the Related Art

FIG. 1 is a block diagram of a transmitter in a Localized FDMA (LFDMA)system being a kind of SC-FDMA system. While the transmitter isconfigured so as to use Discrete Fourier Transform (DFT) and InverseFast Fourier Transform (IFFT) in the illustrated case of FIG. 1, anyother configuration is available to the transmitter.

Referring to FIG. 1, the use of DFT and IFFT facilitates changing LFDMAsystem parameters with low hardware complexity. Concerning thedifference between Orthogonal Frequency Division Multiplexing (OFDM) andSC-FDMA in terms of transmitter configuration, the LFDMA transmitterfurther includes a DFT precoder 101 at the front end of an IFFTprocessor 102 that is used for multi-carrier transmission in an OFDMtransmitter. In FIG. 1, Transmission (TX) modulated symbols 103 areprovided in blocks to the DFT precoder 101. DFT outputs are mapped toIFFT inputs in a band comprised of successive subcarriers. A mapper 104functions to map the transmission modulated symbols to an actualfrequency band.

FIG. 2 illustrates an exemplary data transmission from User Equipments(UEs) in their allocated resources in a conventional SC-FDMA system.

Referring to FIG. 2, one Resource Unit (RU) 201 is defined by one ormore subcarriers in frequency and one or more SC-FDMA symbols in time.For data transmission, two RUs marked with slashed lines are allocatedto UE1 and three RUs marked with dots are allocated to UE2.

The RUs in which UE1 and UE2 transmit data are fixed in time andsuccessive in predetermined frequency bands. This resource allocationscheme or data transmission scheme selectively allocates frequencyresources that offer a good channel status to each UE, to therebymaximize system performance with limited system resources. For example,the slashed blocks offer relatively better radio channel characteristicsto UE1 than in other frequency bands, whereas the dotted blocks offerrelatively better radio channel characteristics to UE2. The selectiveallocation of resources with a better channel response is calledfrequency selective resource allocation or frequency selectivescheduling. As with uplink data transmission from a UE to a Node B asdescribed above, the frequency selective scheduling applies to downlinkdata transmission from the Node B to the UE. On the downlink, the RUsmarked with slashed lines and dots represent resources in which the NodeB transmits data to UE1 and UE2, respectively.

However, the frequency selective scheduling is not always effective. Fora UE that moves quickly and thus experiences a fast change in channelstatus, the frequency selective scheduling is not easy. Morespecifically, although a Node B scheduler allocates a frequency band ina relatively good channel status to a UE at a given time, the UE isplaced in a channel environment that has already changed significantlywhen the UE receives resource allocation information from the Node B andis to transmit data in the allocated resources. Hence, the selectedfrequency band does not ensure the relatively good channel status forthe UE.

Even in a Voice over Internet Protocol (VoIP)-like service that requiresa small amount of frequency resources continuously for datatransmission, if the UE reports its channel status for the frequencyselective scheduling, signaling overhead can be huge. In this case, itis more effective to use frequency hopping rather than the frequencyselective scheduling.

FIG. 3 illustrates an exemplary frequency hopping in a conventional FDMAsystem.

Referring to FIG. 3, frequency resources allocated to a UE for datatransmission change over time. The frequency hopping has the effect ofrandomizing channel quality and interference during data transmission.As data is transmitted in frequency resources that vary over time, thedata has different channel characteristics and a different UE in aneighbor cell interferes with the data at each time point, thusachieving diversity.

However, the frequency hopping is not viable when RUs hop in independentpatterns in the SC-FDMA system as illustrated in FIG. 3. For instance,if RUs 301 and 302 are allocated to different UEs, it does not matter.Yet, if both the RUs 301 and 302 are allocated to a single UE, they hopto the positions of RUs 303 and 304 by frequency hopping at the nexttransmission point. Since the RUs 303 and 304 are not successive, the UEcannot transmit data in these two RUs.

In this context, to achieve frequency diversity in the SC-FDMA system,mirroring is proposed to substitute for the frequency hopping.

FIG. 4 illustrates mirroring.

Conventionally, an RU moves symmetrically with respect to the centerfrequency of a total frequency band available for data transmission. Forexample, an RU 401 is mirrored to an RU 403 and an RU 402 to an RU 404at the next transmission time in Cell A. In the same manner, an RU 405is mirrored to an RU 406 at the next transmission time in Cell B. Themirroring enables successive RUs to hop as successive, therebysatisfying the single carrier property during frequency hopping.

A shortcoming with the frequency hopping with frequency diversity isthat the hopping pattern is fixed because there is no way to move RUswithout mirroring with respect to a center frequency. This means thatfrequency diversity is achieved to a certain degree but interferencerandomization is difficult. As an RU hopped to the opposite returns toits original position by mirroring, only one RU hopping pattern isavailable. Therefore, even when a plurality of cells exist, each cellcannot have a different pattern.

Referring to FIG. 4, if the RU 402 marked with dots is allocated to a UEin Cell A and the RU 405 marked with single-slashed lines is allocatedto a UE in Cell B for a predetermined time, the UE of Cell A interfereswith the UE of Cell B because only one hopping pattern is available inthe mirroring scheme. If the UE of Cell B is near to Cell A, it causesgreat interference to UEs in Cell A. As a result, the UE of Cell A usingRUs marked with dots suffers from reception quality degradation.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least the problemsand/or disadvantages and to provide at least the advantages describedbelow. Accordingly, an aspect of the present invention is to provide amethod and apparatus for allocating resources to randomize interferencebetween neighbor cells when mirroring is adopted to achieve frequencydiversity.

Another aspect of the present invention is to provide a method fordetermining whether to turn on or off mirroring at each hopping timeaccording to a different mirroring on/off pattern for each cell, and atransmitting/receiving apparatus using the same.

A further aspect of the present invention is to provide a method fordetermining whether to turn on or off frequency hopping and mirroring ateach hopping time according to a different pattern for each cell, and atransmitting/receiving apparatus using the same, when frequency hoppingcan be supported to increase a frequency diversity effect.

In accordance with an aspect of the present invention, there is provideda method for allocating resources to a UE in an SC-FDMA communicationsystem, in which inter-subband hopping is performed on a resource unitfor the UE on a frequency axis along which at least two subbands aredefined, at each predetermined hopping time, it is determined whether toturn on or off mirroring in a subband having the hopped resource unit ona cell basis at the each hopping time, and a resource unit is selectedby selectively mirroring the hopped unit according to the determinationand allocated to the UE.

In accordance with another aspect of the present invention, there isprovided a method for being allocated resources from a Node B in anSC-FDMA communication system, in which inter-subband hopping isperformed on a resource unit for a UE on a frequency axis along which atleast two subbands are defined, at each predetermined hopping time, itis determined whether to turn on or off mirroring in a subband havingthe hopped resource unit at the each hopping time according toscheduling information received from the Node B, a resource unit isselected by selectively mirroring the hopped unit according to thedetermination, and data is transmitted in the selected resource unit tothe Node B.

In accordance with a further aspect of the present invention, there isprovided an apparatus of a Node B for allocating resources to UEs in anSC-FDMA communication system, in which a scheduler performsinter-subband hopping on resource units for the UEs on a frequency axisalong which at least two subbands are defined, at each predeterminedhopping time, determining whether to turn on or off mirroring insubbands having the hopped resource units on a cell basis at the eachhopping time, and selects resource units by selectively mirroring thehopped units according to the determination, a mapper separates datareceived from the UEs according to information about the selectedresource units received from the scheduler, and a decoder decodes theseparated data.

In accordance with still another aspect of the present invention, thereis provided an apparatus of a UE for transmitting data to a Node B in anSC-FDMA communication system, in which a data transmission controllerperforms inter-subband hopping on a resource unit for the UE on afrequency axis along which at least two subbands are defined, at eachpredetermined hopping time, and determines whether to turn on or offmirroring in a subband having the hopped resource unit at the eachhopping time according to scheduling information received from the NodeB, and a mapper maps data to a resource unit selected by selectivelymirroring of the hopped resource unit according to the determination andtransmits the data in the mapped resource unit to the Node B.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram of a transmitter in a conventional LFDMAsystem, which is a type of SC-FDMA system;

FIG. 2 illustrates an exemplary data transmission from UEs in theirallocated resources in a conventional SC-FDMA system;

FIG. 3 illustrates an exemplary frequency hopping in a conventional FDMAsystem;

FIG. 4 illustrates mirroring;

FIGS. 5A and 5B illustrate a method according to an exemplary embodimentof the present invention;

FIG. 6 is a flowchart of an operation for selecting RUs in a UE or aNode B according to the exemplary embodiment of the present invention;

FIG. 7 is a block diagram of the UE according to an exemplary embodimentof the present invention;

FIG. 8 is a block diagram of the Node B according to an exemplaryembodiment of the present invention;

FIG. 9 illustrates a channel structure according to another exemplaryembodiment of the present invention;

FIGS. 10A to 10D illustrate a method according to the second exemplaryembodiment of the present invention;

FIG. 11 is a flowchart of an operation for selecting RUs in the UE orthe Node B according to the second exemplary embodiment of the presentinvention;

FIG. 12 illustrates a channel structure according to a third exemplaryembodiment of the present invention;

FIG. 13 illustrates a method for performing mirroring irrespective ofHybrid Automatic Repeat reQuest (HARQ) according to the third exemplaryembodiment of the present invention;

FIG. 14 illustrates a method for performing mirroring for each HARQprocess according to the third exemplary embodiment of the presentinvention; and

FIG. 15 illustrates a method for performing mirroring for each HARQprocess according to a fourth exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofexemplary embodiments of the invention. Accordingly, those of ordinaryskill in the art will recognize that various changes and modificationsof the embodiments described herein can be made without departing fromthe scope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

Exemplary embodiments of the present invention provide a method forincreasing the randomization of interference between cells when data istransmitted in a different RU at each predetermined time by a generalfrequency hopping or mirroring scheme to achieve frequency diversitywhile satisfying the single carrier property in an uplink SC-FDMAsystem.

For a better understanding of the present invention, data channels aredefined as follows:

Frequency Scheduling (FS) band: a set of RUs allocated by frequencyselective scheduling. They are successive or scattered.

Frequency Hopping (FH) band: a set of RUs transmitted to achievefrequency diversity. These RUs are not allocated by frequency selectivescheduling. They are successive or scattered. An FH band can becomprised of one or more sub-FH bands.

Mirroring: RUs are symmetrically hopped from left to right and fromright to left with respect to a center subcarrier or a center RU in asub-FH band.

Hopping time: a time at which an allocated RU hops or is mirrored.Depending on how hopping or mirroring applies, the RU has the followingperiod.

1. When intra-subframe hopping and inter-subframe hopping are supported,the period is a slot.

2. When only inter-subframe hopping is supported, the period is onesub-frame.

Embodiment 1

An exemplary embodiment of the present invention provides a method forturning mirroring on or off according to a different mirroring on/offpattern for each cell. Using different mirroring on/off patterns fordifferent cells as much as possible and decreasing the probability ofmirroring-on in cells at the same time maximize the effect ofrandomizing interference between cells.

FIGS. 5A and 5B illustrate a method according to the exemplaryembodiment of the present invention. FIG. 5A illustrates slot-basedmirroring irrespective of Hybrid Automatic Repeat reQuest (HARQ) andFIG. 5B illustrates independent mirroring for each HARQ process.

Referring to FIG. 5A, there are cells 501 and 502 (Cell A and Cell B).As intra-subframe hopping is assumed, the hopping period is a slot. On aslot basis, mirroring is performed at each hopping time in a pattern 503of on, on, on, off, on, off, off, off . . . in Cell A, and in a pattern512 of on, off, on, on, off, off, on, on, . . . in Cell B.

In Cell A, an RU 504 is allocated to UE A at hopping time k. Sincemirroring is on for UE A at the next hopping time (k+1), UE A uses an RU505 in slot (k+1). Mirroring is off at hopping time (k+3) and thus UE Atransmits data in an RU 506 identical to an RU used in the previous slot(k+2) in slot (k+3). Similarly, since mirroring is off at hopping time(k+6), UE A transmits data in an RU 507 identical to an RU transmittedin the previous slot (k+5) in slot (k+6).

In the same manner, an RU 508 is allocated to UE B in slot k in Cell B.Since mirroring is off at the next hopping time (k+1), UE B uses an RU509 in slot (k+1). At hopping time (k+3), mirroring is on and thus UE Buses an RU 510 in slot (k+3). Similarly, since mirroring is on athopping time (k+6), UE B uses an RU 511 in slot (k+6).

Mirroring is on or off at each hopping time in a different pattern ineach cell. Therefore, while UEs within different cells may use the sameRU in a given slot, the probability of the different cells using thesame RU in the next slot decreases due to the use of different mirroringon/off patterns. For example, the RUs 504 and 508 are allocatedrespectively to UE A in Cell A and UE B in Cell B in slot k. If UE B isnear to Cell A, UE B will likely significantly interfere with UE A.However, since UE A turns on mirroring at the next hopping time (k+1),UE A transmits data in the RU 505 in slot (k+1), whereas mirroring isoff for UE B and thus UE B transmits data in the RU 509 identical tothat used in the previous slot. Thus, UE A and UE B use different RUs inslot (k+1).

The mirroring method illustrated in FIG. 5B is similar to thatillustrated in FIG. 5A in that different cells use different mirroringon/off patterns and the former method illustrated in 5B differs from thelatter method illustrated in 5A in that an RU is mirrored with respectto an RU in the same HARQ process rather than with respect to an RU inthe previous slot. In FIG. 5B, mirroring is on for a UE in a cell 513(Cell A) at hopping time k. Thus, the UE uses an RU 518 to which an RU517 used in the previous slot (k-RTT+1) of the same HARQ process ismirrored, instead of an RU to which an RU used in the previous slot(k−1) is mirrored. RTT represents Round Trip Time, defined as the timetaken for an initial transmission in the case where a response fortransmitted data is a Negative ACKnowledgment (NACK) and a response forretransmitted data is an ACK. Therefore, data transmitted in RUs 518 and519 are retransmission versions of data transmitted in RUs 516 and 517or belong to the same HARQ process as the data transmitted in the RUs516 and 517. The HARQ RTT-based mirroring facilitates defining amirroring on/off pattern in which different RUs are used for initialtransmission and retransmission. Despite this advantage, management of adifferent mirroring on/off pattern for each HARQ process increasescomplexity. In this context, a mirroring on/off pattern is determined asfollows.

(1) Mirroring is on/off at each hopping time according to apredetermined sequence. The sequence is needed to indicate whethermirroring is on or off, not to indicate the position of an RU forhopping. Therefore, the sequence is composed of two values. In general,a binary sequence is composed of 0s or 1s.

(2) A plurality of sequences are generated and allocated to cells suchthat different patterns are applied to at least neighbor cells tothereby minimize RU collision among them. For example, a set oforthogonal codes such as Walsh codes are allocated to respective cellsand each cell determines mirroring on/off according to a code value 0 or1 at each hopping time. Alternatively, each cell can determine mirroringon/off according to a Pseudo Noise (PN) sequence having a seed specificto the cell. As compared to the former method, the latter methodincreases randomization between cells and thus minimizes the phenomenonin which RUs hop in the same manner in different cells. In the contextof the PN sequence-based method, the exemplary embodiment of the presentinvention will be described below.

For generation of a PN sequence, a cell-specific seed is used and toachieve the same PN sequence, UEs within the same cell should receivethe same timing information. The timing information can be representedas the difference between an absolute time and a current time or as acommon time frame count such as a System Frame Number (SFN).

FIG. 6 is a flowchart of an operation for determining mirroring on/offin a UE according to the exemplary embodiment of the present invention.To receive data from the UE, a Node B can perform the same operation.

Referring to FIG. 6, when the Node B schedules an RU for the UE, the UEgenerates a PN sequence value in step 601 and checks the PN sequencevalue in step 602. If the PN sequence value is 0, the UE turns mirroringoff in step 604. If the PN sequence value is 1, the UE turns mirroringon in step 603. In step 605, the UE selects an RU for the next datatransmission according to the mirroring-on/off decided in step 603 or604. The UE transmits data in the selected RU in step 606.

Mirroring results in a symmetrical RU hopping with respect to the centerJ2 of a total FH band. A new RU for use in the next slot can be detectedbased on information about an RU used in a previous slot. The mirroringis expressed as Equation (1):

H(r)=N _(FH) −r   . . . (1)

where r denotes an RU being a mirroring base. The mirroring base is anRU used in the previous slot in FIG. 5A and an RU used in the previousslot of the same HARQ process in FIG. 5B. H(r) denotes an RU to whichthe mirroring base is mirrored in a slot. N_(FH) denotes the totalnumber of RUs in the FH band.

FIG. 7 is a block diagram of the UE according to the exemplaryembodiment of the present invention.

Referring to FIG. 7, a data symbol generator 703 generates data symbolsto be transmitted. The amount of data transmittable in each TransmissionTime Interval (TTI) is determined by Node B scheduling. ASerial-to-Parallel (S/P) converter 704 converts the sequence of the datasymbols to parallel symbol sequences. A DFT processor 705 converts theparallel symbol sequences to frequency signals, for SC-FDMAtransmission. A DFT size is equal to the number of the data symbolsgenerated from the data symbol generator 703. A mapper 706 maps thefrequency signals to frequency resources allocated to the UE based on RUinformation received from a data transmission controller 702. The datatransmission controller 702 generates the RU information based onscheduled RU information and mirroring on/off information. Each cell hasa different mirroring on/off pattern according to a PN sequence. Hence,a PN sequence generator 701 is required. An RU to be used is decidedusing the output of the PN sequence generator 701 in the afore-describedmethod. An IFFT processor 707 converts the mapped signals to timesignals. A Parallel-to-Serial (P/S) converter 708 converts the timesignals to a serial signal for transmission.

FIG. 8 is a block diagram of the Node B according to the exemplaryembodiment of the present invention.

Referring to FIG. 8, an S/P converter 807 converts a received signal toparallel signals and an FFT processor 806 converts the parallel signalsto frequency signals. A demapper 805 demaps the frequency signals fordifferent UEs based on RU allocation information about each UEdetermined by an uplink scheduler 802. The uplink scheduler 802generates the RU information for each UE using scheduled RU informationand mirroring on/off information based on a mirroring on/off pattern.Since each cell has a different mirroring on/off pattern, a PN sequencegenerator 801 is needed. An RU from which data is to be extracted isdecided based on the output of the PN sequence generator 801 in theafore-described method. An IDFT processor 804 converts the demappedsignal of an intended UE, UE 1 to time signals. A P/S converter 808converts the time signals to a serial signal. A data symbol decoder 803demodulates data received from UE 1.

Embodiment 2

Inter-sub-FH band hopping on/off is combined with mirroring on/off, andthe position of an RU for data transmission is determined by selectingone of the combinations such that each cell has a different pattern.That is, the resources of a total system frequency band is divided intoan FH band and an FS band and a channel structure is proposed, whichoffers a sufficient frequency hopping gain in the FH band and achieves asufficiently available frequency band in the FS band.

FIG. 9 illustrates the channel structure according to the secondexemplary embodiment of the present invention.

Referring to FIG. 9, sub-FH bands 901 and 903 are defined at either sideof a total frequency band and the center frequency band between thesub-FH bands 901 and 903 is defined as an FS band 902. UEs using the FSband 902 can hop to the sub-FH bands 901 and 903, thereby achieving asufficient frequency hopping gain. As the frequencies of the FS band 902are successive to maximize successive frequency allocation, a maximumdata rate can be increased.

A method for performing inter-sub-FH band hopping and mirroring withineach FH band in order to achieve a sufficient frequency diversity gainand simultaneously to enable variable RU allocation, taking into accountthe single carrier property in the proposed channel structure will nowbe described. As done in the first exemplary embodiment of the presentinvention, inter-sub-FH band hopping is on/off and mirroring is on/offat each hopping time according to a cell-specific pattern.

Four combinations of inter-sub-FH band hopping on/off and mirroringon/off are available as illustrated in Table 1. At each hopping time,one of the combinations is selected and hopping or/and mirroring applyto each cell using the selected combination in a different pattern.

TABLE 1 Combination FH band hopping Mirroring 1 On On 2 Off Off 3 Off On4 On Off

FIGS. 10A to 10D describe the second exemplary embodiment of the presentinvention.

FIGS. 10A and 10B are based on the assumption that intra-TTI hopping issupported in cells 1001 and 1007 (Cell A and Cell B). Therefore, thehopping period is a slot.

Referring to FIGS. 10A and 10B, combinations of inter-sub-FH bandhopping on/off and mirroring on/off according to Table 1 are selected inthe order of 3-1-4-3-2-1-2-3 for Cell A and in the order of3-4-2-1-3-2-1-4 for Cell B.

Although Cell A uses an RU 1002 at hopping time k, it selects an RU 1005by inter-sub-FH band hopping and mirroring according to combination 1 athopping time (k+1). At the next hoping time (k+2), Cell A performs onlyinter-sub-FH band hopping without mirroring according to combination 4and thus selects an RU 1003. Since combination 2 is set for hopping time(k+4), Cell A selects an RU 1004 without inter-sub-FH band hopping andmirroring.

Cell B selects the same RU 1008 used for Cell A at hopping time k. Athopping time (k+1), Cell B selects an RU 1009 through inter-sub-FH bandhopping only without mirroring according to combination 4, as comparedto Cell A that selects the RU 1005 through both inter-sub-FH bandhopping and mirroring according to combination 1. While another UEwithin Cell B may use the same RU as the RU 1005 in slot (k+1),interference from a different UE at each time rather than collision withthe same UE offers a better interference randomization gain.

In the illustrated cases of FIGS. 10C and 10D, inter-sub-FH band hoppingand mirroring are carried out with respect to an RU used for theprevious data transmission of the same HARQ process, instead of an RUused at the previous hopping time.

Referring to FIG. 10C, an RU 1013 is selected at hopping time k byinter-sub-FH band hopping of an RU 1014 used for the previous datatransmission of the same HARQ process, not of an RU used at hopping time(k−1). Combination 4 is set for hoping time k, which means inter-sub-FHband hopping is on and mirroring is off with respect to the RU 1014.Thus, the RU 1013 is selected at hopping time k. At hopping time (k+1)for which combination 3 is set, the RU 1013 is inter-sub-FH band-hoppedand mirrored to an RU 1012.

A method for selecting combinations of inter-sub-FH band hopping on/offand mirroring on/off using a predetermined sequence will now bedescribed.

(1) Since the sequence is needed to indicate combinations selected fromthe four combinations of inter-sub-FH band hopping on/off and mirroringon/off, but the sequence is not needed to indicate the position of an RUfor hopping, four values are available in forming the sequence. Ingeneral, a quaternary sequence or two binary sequences in combinationserves the purpose of indicating selected combinations. The sequence canbe generated in a conventional method and thus a detailed description ofthe method is not provided herein.

(2) A plurality of sequences are generated and allocated to cells suchthat different patterns are applied to at least neighbor cells tothereby minimize RU collision among them. For example, a set oforthogonal codes such as Walsh codes are allocated to cells in aone-to-one correspondence and each cell selects a combination accordingto a sequence value at each hopping time. Alternatively, each cell canselect a combination according to a PN sequence having a seed specificto the cell. As compared to the former method, the latter methodincreases randomization between cells and thus minimizes RUs hopping inthe same manner in different cells. In the context of the PNsequence-based method, the exemplary embodiment of the present inventionwill be described below.

For generation of a PN sequence, a cell-specific seed is used and toachieve the same PN sequence, UEs within the same cell should receivethe same timing information. The timing information can be representedas the difference between an absolute time and a current time or as acommon time frame count such as an SFN.

FIG. 11 is a flowchart of an operation of the UE according to the secondexemplary embodiment of the present invention. The same operationapplies to the Node B when it receives data from the UE.

Referring to FIG. 11, when the Node B schedules a specific RU for theUE, the UE generates a PN sequence value in step 1101 and determineswhether the PN sequence value is 1, 2, 3, or 4 in step 1102. If the PNsequence value is 1, the UE selects a combination of mirroring-on andinter-sub-FH band hopping-on in step 1103. If the PN sequence value is2, the UE selects a combination of mirroring-off and inter-sub-FH bandhopping-off in step 1104. If the PN sequence value is 3, the UE selectsa combination of mirroring-off and inter-sub-FH band hopping-on in step1105. If the PN sequence value is 4, the UE selects a combination ofmirroring-on and inter-sub-FH band hopping-off in step 1106. In step1107, the UE selects an RU for data transmission by mirroring and/orhopping according to the selected combination. The UE transmits data inthe selected RU in step 1108.

A transmitter and a receiver according to the second exemplaryembodiment of the present invention have the same configurations asthose according to the first exemplary embodiment of the presentinvention, except that the PN sequence generators 701 and 802 generateone of four values 1 to 4 and provide the generated value to the datatransmission controller 702 and the uplink scheduler 802 so as todetermine the position of an RU.

Embodiment 3

FIG. 12 illustrates a channel structure according to a third exemplaryembodiment of the present invention.

For a system where a plurality of sub-FH bands exist as illustrated inFIG. 12 and where hopping always occurs between the sub-FH bands, amethod is proposed for determining mirroring on/off according to adifferent pattern for each cell. The use of different mirroring on/offpatterns for different cells decreases the probability of performingmirroring at the same time in the different cells, thus resulting inmaximized randomization of inter-cell interference.

FIGS. 13 and 14 describe a method according to a third exemplaryembodiment of the present invention. Specifically, FIG. 13 illustrates amirroring method independent of HARQ and FIG. 14 illustrates a methodfor performing mirroring on an HARQ process basis.

Referring to FIG. 13, since it is assumed that both cells 1301 and 1311(Cell A and Cell B) support intra-subframe hopping, the hopping periodis a slot. Mirroring is performed at each hopping time in a pattern 1310of on, on, off, off, on, off, off, off . . . in Cell A, and in a pattern1320 of on, off, off, on, off, off, on, on, . . . in Cell B.

If an RU 1302 in sub-FH band #1 is allocated to a UE at hopping time kin Cell A, it hops to sub-FH band #2 occurs because inter-sub-FH bandhopping applies always and is mirrored according to the mirroringpattern 1310. Hence, the UE uses an RU 1303 in slot (k+1). At the nexthopping time (k+2), the UE selects an RU 1304 through hopping to sub-FHband #1 and mirroring-off. Since hopping to sub-FH band #2 occurs andmirroring is off at the next hopping time (k+3), the UE uses an RU 1305in slot (k+3).

Compared to Cell A, a different mirroring on/off pattern is defined forCell B. In other words, mirroring is on/off in a different manner ateach hopping time for each cell. Although Cell A and Cell B may selectthe same RU at a given hopping time, the third exemplary embodiment ofthe present invention reduces the probability of selecting the same RUat the next hopping time in the two cells.

For instance, in the case where the same RUs 1302 and 1312 are allocatedrespectively to UE A in Cell A and UE B in Cell B for a predeterminedtime, if UE B is near to Cell A, UE A is probable to be interferedsignificantly by UE B at hopping time k. However, since Cell A performsboth inter-sub-FH band hopping and mirroring at the next hopping time(k+1), UE A transmits data in the RU 1303 in slot (k+1), whereasinter-sub-FH band hopping is on and mirroring is off for UE B and thusUE B transmits data in an RU 1313 in slot (k+1). Thus, UE A and UE B usedifferent RUs in slot (k+1), thus avoiding continual interference fromthe same UE.

The mirroring method illustrated in FIG. 14 is similar to thatillustrated in FIG. 13 in that mirroring follows inter-sub-FH bandhopping and different cells use different mirroring on/off patterns, andthe former differs from the latter in that an RU is mirrored withrespect to an RU in the same HARQ process rather than with respect to anRU used at the previous transmission time.

That is, at hopping time (k+RTT), a UE in a cell 1401 (Cell A) uses anRU 1407 to which an RU 1406 used in slot (k+1) of the same HARQ processis mirrored, instead of an RU to which an RU used in the previous slot(k+RTT−1) is mirrored. The HARQ RTT-based mirroring facilitates defininga mirroring on/off pattern in which different RUs are used for initialtransmission and retransmission, thereby maximizing an interferencediversity effect.

The UE determines mirroring on/off in the same manner as in the firstexemplary embodiment of the present invention, except that inter-sub-FHband hopping occurs all the time in selecting an RU.

To realize the third exemplary embodiment of the present invention, ahopping pattern formula is given as Equation (2), for example. The UE isaware of a resource block to be used at each transmission time using thehopping pattern formula and the index of a scheduled resource block.Equation (2) uses sub-band-based shifting for inter-subband hopping.

$\begin{matrix}{{{O_{s} = {{f\_ s} - {N_{o} \cdot {h(t)}}}},{O_{s} = {O_{s}\mspace{11mu} {mod}\; {N\_ RB}}}}{{{if}\mspace{14mu} 0} \leq O_{s} < N_{s}}{{f_{hop}(i)} = {{N_{o} \cdot {h(i)}} + O_{s} + {\left\{ {\left( {N_{s} - 1} \right) - {2 \times \left( {O_{s}\mspace{11mu} {{mod}\left( N_{s} \right)}} \right)}} \right\} \times {m(i)}}}}{{f_{hop}(i)} = {{f_{hop}(i)}{mod}\; {N\_ RB}}}{{{else}\mspace{14mu} {if}\mspace{14mu} N_{s}} \leq O_{s}}{{f_{hop}(i)} = {{N_{o} \cdot {h(i)}} + O_{s} + {\left\{ {\left( {N_{o} - 1} \right) - {2 \times \left( {\left( {O_{s} - N_{s}} \right){{mod}\left( N_{o} \right)}} \right)}} \right\} \times {m(i)}}}}{{f_{hop}(i)} = {{f_{hop}(i)}{mod}\; {N\_ RB}}}} & (2)\end{matrix}$

where O_(s) denotes an offset by which a resource block scheduled to theUE is spaced from a cyclic shift reference point, f_s denotes the indexof a resource block allocated by a scheduling grant, h(t) denotes thedegree to which the scheduled resource block is cyclically shifted atscheduling time (t), f_(hop)(i) denotes the index of a resource blockafter hopping at hopping time (i), N_RB denotes the total number ofresource blocks available for data transmission, and N_(o) and N_(s) aremaximum numbers of resources blocks that can be scheduled for UEs thatperform hopping.

If the total number of resource blocks N_RB is not a multiple of thenumber of subbands M, a particular subband has a fewer number ofresource blocks, N_(s) than that of the resource blocks of the othersubbands each N_(o). Because Equation (2) assumes that only one subbandhas a fewer number of resource blocks, N_(o) and N_(s) are computed byEquation (3):

$\begin{matrix}{{N_{o} = \left\lceil \frac{N\_ RB}{M} \right\rceil},{N_{s} = {{N\_ RB} - {\left( {M - 1} \right) \times N_{o}}}}} & (3)\end{matrix}$

In Equation (2), h(i) denotes a cyclic shift degree, being one of {0, 1,. . . , M} selected according to a bit value of a random sequence.h(o)=0. m(i) is a parameter that determines mirroring on/off at hoppingtime (i), being one of {0, 1}. m(i) is selected according to a bit valueof a random sequence, or by h(i)=x/2 and m(i)=xMod(2) where x is one of{0, 1, . . . , M} selected according to the bit value of the randomsequence. If m(i)=0, mirroring is off and if m(i)=1, mirroring is on.

To describe Equation (2) in great detail, the offset O_(s) at thescheduling time of the scheduled resource block, is first calculated bythe first line of Equation (2). O_(s) indicates how far a cyclicallyshifted resource block is spaced from the cyclic shift reference point.

O_(s) is introduced for the following reason. When the total number ofresource blocks N_RB is not a multiple of the number of subbands M, thesubbands do not have the same amount of resources, causing failedinter-subband hopping. Therefore, subbands are formed such that onesubband has a fewer number of resource blocks N_(o) than the numberN_(s) of resources blocks of each of the other subbands and O_(s) usedto indicate the subband having the fewer number of resource blocks tothe UE in the third exemplary embodiment of the present invention.

For example, if N_RB is 22 and M is 4, subbands can be configured sothat a first subband has four resource blocks and each of the othersubbands has six resource blocks. In this subband structure, if O_(s) isless than 4, the UE is aware that the scheduled resource block residesin the smaller subband.

According to the first conditional sentence of Equation (2), then, thescheduled resource block is cyclically shifted with respect to resourceblocks 0 to N_(s)−1 according to the offset O_(s) and then mirroredwithin N_(s) resource blocks. If m(i)=0, mirroring is off.

If O_(s) is larger than N_(s), which implies that the scheduled resourceblock resides in a normal subband, a cyclic shift is performed accordingto the second conditional sentence of Equation (2) and then mirroring isperformed within N_(o) resource blocks. If m(i)=0, mirroring is off.

Depending on a subband configuration, a plurality of subbands may eachhave N_(s) resource blocks with a plurality of remaining subbands eachhaving N_(o) resource blocks. For example, if four subbands are given,two subbands each have five resources blocks and the other two subbandseach include six resource blocks. This case can be easily realized bymodifying the conditional sentences of Equation (2) that indicate ascheduled subband using an offset.

Embodiment 4

If mirroring is on or off according to a random pattern in each cell,successive mirroring ons/offs increase the probability of datatransmission from UEs in the same RUs in different cells. Consideringthat it is preferred, in terms of channel quality, to achieve asufficient frequency diversity at each transmission time when data istransmitted by an HARQ process, it is necessary to allow UEs to selectdifferent RUs at least under a successive data transmission situationsuch as initial transmission and retransmission. To do so, a fourthexemplary embodiment of the present invention proposes a limited use ofa method for generating a random mirroring pattern and determiningmirroring on/off according to the random mirroring pattern, when needed.When both intra-subframe hopping and inter-subframe hopping aresupported, mirroring is always on at each hopping time for one of thetwo hopping schemes and mirroring is on/off in a random mirroring on/offpattern for the other hopping scheme.

FIG. 15 illustrates a method for always turning on mirroring forinter-subframe hopping and determining mirroring on/off according to arandom mirroring on/off pattern for intra-subframe hopping according tothe fourth exemplary embodiment of the present invention.

As in the second exemplary embodiment of the present invention, sub-FHbands are positioned at either side of a system frequency band and an FSband is interposed at the center frequency band between the sub-FHbands. To achieve a frequency diversity gain, an RU hops between thesub-FH bands at each hopping time as in the third exemplary embodimentof the present invention.

Referring to FIG. 15, mirroring occurs at each intra-subframe hoppingtime according to a pattern of on, off, off, . . . in a cell 1500 (CellA) and according to a pattern of off, off, on, . . . in a cell 1520(Cell B).

When an RU 1502 is allocated to a UE at hopping time (k-RTT) in Cell A,the UE selects an RU 1503 by mirroring according to the mirroring on/offpattern at the next hopping time (k-RTT+1). At hopping time k being thenext transmission time of the same HARQ process, mirroring is always on.To select an RU at a different position from an RU transmitted at theprevious transmission time of the same HARQ process, an RU 1504 isselected by mirroring the RU 1502 used in the first slot (k-RTT) of theprevious HARQ transmission time. Since mirroring is off according to themirroring on/off pattern at the next hopping time (k+1), the UE selectsan RU 1505. At hopping time (k+RTT) being the next transmission time ofthe same HARQ process, mirroring is always on. To select an RU at adifferent position from an RU transmitted at the previous HARQtransmission time, the RU 1504 is mirrored to an RU 1506. Sincemirroring is off according to the mirroring on/off pattern at the nexthopping time (k+RTT+1), the UE selects an RU 1507.

In the same manner, an RU hops to another sub-FH band by turning on/offmirroring according to a random mirroring on/off pattern at eachintra-subframe hopping time in Cell B. That is, if an RU 1508 is used inslot (k-RTT), an RU 1509 is selected by turning off mirroring accordingto the mirroring on/off pattern at the next hopping time (k-RTT+1).Since mirroring is performed with respect to the RU 1508 used at theprevious transmission time of the same HARQ process at the next HARQtransmission time, an RU 1510 is selected at hopping time k. At hoppingtime (k+1), mirroring is off according to the mirroring on/off patternand thus an RU 1511 is selected. Since mirroring is performed withrespect to the RU 1510 used at the previous transmission time of thesame HARQ process at the next HARQ transmission time, an RU 1512 isselected at hopping time (k+RTT). At hopping time (k+RTT+1), mirroringis on according to the mirroring on/off pattern and thus an RU 1513 isselected.

As is apparent from the above description, the present inventionadvantageously randomizes inter-cell interference, increasing afrequency diversity effect, by turning on or off mirroring at eachhopping time according to a different mirroring on/off pattern in eachcell.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the present invention as defined by the appended claims andtheir equivalents.

1. A method for allocating resources to a User Equipment (UE) in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) communication system, comprising: performing inter-subband hopping on a resource unit for the UE on a frequency axis along which at least two subbands are defined, at each predetermined hopping time; determining whether to turn on or off mirroring in a subband having the hopped resource unit on a cell basis at the each hopping time; and selecting a resource unit by selectively mirroring the hopped resource unit according to the determination and allocating the selected resource unit to the UE.
 2. The method of claim 1, further comprising generating sequences each indicating mirroring-on or mirroring-off at a plurality of hopping times and allocating the sequences to cells, before the selective mirroring, wherein the determination comprises determining whether to turn on or off the mirroring according to a bit value of a sequence allocated on a cell basis.
 3. The method of claim 1, wherein the resource unit for the UE is one of a resource unit allocated to the UE at a previous hopping time and a resource unit used for a previous transmission of a same Hybrid Automatic Repeat reQuest (HARQ) process for data.
 4. The method of claim 2, wherein each of the sequences is one of a cell-specific orthogonal code selected from a set of orthogonal codes and a Pseudo-Noise (PN) sequence having a cell-specific seed.
 5. The method of claim 1, further comprising, if the subbands have different numbers of resource units, determining mirroring-on or mirroring-off along the frequency axis within the subband having the resource unit for the UE on a cell basis, at the each hopping time; determining a position to which the resource unit for the UE is to hop according to an index of the resource unit; and selecting a resource unit by performing frequency hopping and mirroring according to the determined position and the determined mirroring-on or mirroring-off and allocating the selected resource unit to the UE.
 6. The method of claim 1, wherein the selective mirroring comprises always performing mirroring at predetermined inter-subframe hopping times and selectively performing mirroring at intra-subframe hopping times according to the determination.
 7. A method for being allocated resources from a Node B in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) communication system, comprising: performing inter-subband hopping on a resource unit for a User Equipment (UE) on a frequency axis along which at least two subbands are defined, at each predetermined hopping time; determining whether to turn on or off mirroring in a subband having the hopped resource unit at the each hopping time according to scheduling information received from the Node B; and selecting a resource unit by selectively mirroring the hopped resource unit according to the determination and transmitting data in the selected resource unit to the Node B.
 8. The method of claim 7, wherein the determination comprises determining whether to turn on or off mirroring the hopped resource unit according to a bit value of a cell-specific sequence indicating mirroring-on or mirroring-off at a plurality of hopping times, received from the Node B.
 9. The method of claim 7, wherein the resource unit for the UE is one of a resource unit allocated to the UE at a previous hopping time and a resource unit used for a previous transmission of a same Hybrid Automatic Repeat reQuest (HARQ) process for data.
 10. The method of claim 8, wherein the sequence is one of a cell-specific orthogonal code selected from a set of orthogonal codes and a Pseudo-Noise (PN) sequence having a cell-specific seed.
 11. The method of claim 7, wherein the selective mirroring comprises always performing mirroring at predetermined inter-subframe hopping times and selectively performing mirroring at intra-subframe hopping times according to the determination.
 12. The method of claim 7, further comprising, if the subbands have different numbers of resource units, determining mirroring-on or mirroring-off along the frequency axis within the subband having the resource unit for the UE on a cell basis at the each hopping time according to the scheduling information received from the Node B; determining a position to which the resource unit for the UE will hop according to the index of the resource unit; and selecting a resource unit by performing frequency hopping and mirroring according to the determined position and the determined mirroring-on or mirroring-off and transmitting data in the selected resource unit to the Node B.
 13. An apparatus of a Node B for allocating resources to User Equipments (UEs) in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) communication system, comprising: a scheduler for performing inter-subband hopping on resource units for the UEs on a frequency axis along which at least two subbands are defined, at each predetermined hopping time, determining whether to turn on or off mirroring in subbands having the hopped resource units on a cell basis at the each hopping time, and selecting resource units by selectively mirroring the hopped resource units according to the determination; a mapper for separating data received from the UEs according to information about the selected resource units received from the scheduler; and a decoder for decoding the separated data.
 14. The apparatus of claim 13, further comprising a sequence generator for generating sequences for cells, each indicating mirroring-on or mirroring-off at a plurality of hopping times, wherein the scheduler determines whether to turn on or off mirroring according to bit values of the sequences allocated on a cell basis.
 15. The apparatus of claim 13, wherein the scheduler performs mirroring with respect to one of resource units allocated to the UEs at a previous hopping time and resource units used for a previous transmission of a same Hybrid Automatic Repeat reQuest (HARQ) process for data.
 16. The apparatus of claim 14, wherein the sequence generator generates cell-specific orthogonal codes for the cells from a set of orthogonal codes or Pseudo-Noise (PN) sequences having cell-specific seeds for the cells.
 17. The apparatus of claim 13, wherein the scheduler always performs mirroring at predetermined inter-subframe hopping times and selectively performs mirroring at intra-subframe hopping times according to the determination.
 18. The apparatus of claim 13, wherein if the subbands have different numbers of resource units, the scheduler determines mirroring-on or mirroring-off along the frequency axis within the subbands having the resource units for the UEs on a cell basis, at the each hopping time, determines positions to which the resource units for the UEs are to hop according to the indexes of the resource units, and selects resource units for the UEs by performing frequency hopping and mirroring according to the determined positions and the determined mirroring-on or mirroring-off.
 19. An apparatus of a User Equipment (UE) for transmitting data to a Node B in a Single Carrier-Frequency Division Multiple Access (SC-FDMA) communication system, comprising: a data transmission controller for performing inter-subband hopping on a resource unit for the UE on a frequency axis along which at least two subbands are defined, at each predetermined hopping time, and determining whether to turn on or off mirroring in a subband having the hopped resource unit at the each hopping time according to scheduling information received from the Node B; and a mapper for mapping data to a resource unit selected by selective mirroring of the hopped resource unit according to the determination and transmitting the data in the mapped resource unit to the Node B.
 20. The apparatus of claim 19, wherein the data transmission controller determines whether to turn on or off mirroring the hopped resource unit according to a bit value of a cell-specific sequence indicating mirroring-on or mirroring-off at a plurality of hopping times, received from the Node B, further comprising a sequence generator for generating the sequence.
 21. The apparatus of claim 19, wherein the data transmission controller performs mirroring on a resource unit allocated to the UE at a previous hopping time or a resource unit used for a previous transmission of a same Hybrid Automatic Repeat reQuest (HARQ) process for data.
 22. The apparatus of claim 20, wherein the sequence generator generates one of a cell-specific orthogonal code selected from a set of orthogonal codes and a Pseudo-Noise (PN) sequence having a cell-specific seed.
 23. The apparatus of claim 19, wherein the data transmission controller always performs mirroring at predetermined inter-subframe hopping times and selectively performs mirroring at intra-subframe hopping times according to the determination.
 24. The apparatus of claim 19, wherein if the subbands have different numbers of resource units, the data transmission controller determines mirroring-on or mirroring-off along the frequency axis within the subband having the resource unit for the UE on a cell basis at the each hopping time according to the scheduling information received from the Node B, determines a position to which the resource unit for the UE is to hop according to the index of the resource unit, and performs frequency hopping and mirroring according to the determined position and the determined mirroring-on or mirroring-off. 